Abstract

Prostate cancer (PCa) is an increasing worldwide health issue. Broadly, PCa is composed of two main forms, latent organ confined and aggressive metastatic. While therapeutic options for the latent form are available and effective, therapeutics for metastatic PCa are limited to androgen deprivation therapy (ADT), whose efficacy is short-lived. In the early stages, PCa cells regress upon androgen withdrawal, however, after a short period of time the cells acquire the ability to thrive in an environment of low androgens, known as androgen independence. This progression is one of the well recognised hallmarks of cancer, which also includes the acquisition of insensitivity to negative growth signals. A crucial negative growth regulator in the prostate is activin A, a member of the TGF-β superfamily. Activin A in low-grade PCa can inhibit cancer progression via promoting apoptosis and decreasing cell proliferation. However, in aggressive PCa the cells acquire insensitivity to the growth inhibitory effects of activin A, a situation resembling androgen independence. Hence, activin A insensitivity is an acquired capability in PCa, of which the underlying mechanisms are currently not well understood. Non-coding RNA, MicroRNAs (miRNA), play a crucial role in cellular processes via negatively regulating genes at the level of translation. No studies have investigated the effect of activin A on miRNA expression in PCa, creating a significant void in PCa biology.

Therefore, the aim of this study was to investigate the effect of activin A on miRNA expression in LNCaP cells which are highly sensitive to activin A. Pathway-focused RT-qPCR arrays were utilized to assess miRNA expression following activin A treatment. Activin A significantly altered 9 miRNA; miR-222/15b/93/18a/let-7i were decreased while miR-30a/30d/let-7c/196b were increased compared to media control. To investigate the effect of the significantly altered miRNA on biological signaling pathways, miRPath pathway enrichment was conducted. These 9 miRNA were found to be targeting elements of pathways, including, PI3K-Akt, MAPK, cell cycle, PCa, and TGF-β. Western blots were conducted for proteins of the cell cycle pathway. Ki67 and PCNA have been shown to be dysregulated in PCa progression and are validated targets of miR-196b/let-7c and miR-30a/30d respectively. Protein levels of Ki67 and PCNA were significantly decreased upon activin A treatment, which correlated with increased levels of miR-196b/let-7c and miR-30a/30d.

In conclusion, this study has identified for the first time activin A-mediated miRNAs in LNCaP cells. Like other TGF-β superfamily members where modulation of signaling has demonstrated therapeutic potential, alteration of activin A mediated miRNAs could provide a novel therapeutic for advanced prostate cancer.